Aliphatic esters of carboxymethene- and carboxyethenethiosuccinic acid

ABSTRACT

Aliphatic esters of carboxymethene- and carboxyethenethiosuccinic acid are readily prepared in a two-step process comprising (a) the addition reaction between mercaptoacetic or mercaptopropionic acid and butenedioic anhydride to form an acid-anhydride intermediate, and (b) the esterification of the intermediate using monohydric aliphatic alcohols to form the trisester products. The compounds are used with phenol anti-oxidants to provide excellent protection against oxidation of polymers, especially polyolefins.

United States Patent 1 Gilles 1 1 Sept. 30, 1975 [54] ALIPHATIC ESTERSOF CARBOXYMETHENE- AND CARBOXYETHENETHIOSUCCINIC ACID [75] lnventor:Jack C. Gilles, Shaker Heights, Ohio [73] Assignee: The B. F. GoodrichCompany,

Akron, Ohio [22] Filed: Aug. 24, 1973 [21] Appl. No.: 391,220

Related US. Application Data [62] Division of $81. No. 191.491. Oct. 2i.

abandoned.

[52] U.S. Cl...... 260/45.7 S; 260/45.85 S; 260/93.7;

FOREIGN PATENTS OR APPLICATIONS 40-13257 6/1965 Japan 260/94.9 GD

Primary Examiner.loseph L. Schofer Assistant Examiner-A. HollerAttorney, Agent, or Firm.l. Hughes Powell, Jr.; Alan A. Csontos 5 7ABSTRACT Aliphatic esters of carboxymetheneand carboxyethenethiosuccinicacid are readily prepared in a two-step process comprising (a) theaddition reaction between mercaptoacetic or mercaptopropionic acid andbutenedioic anhydride to form an acidanhydride intermediate, and (b) theestcrification of the intermediate using monohydric aliphatic alcoholsto form the trisester products. The compounds are used with phenolanti-oxidants to provide excellent protection against oxidation ofpolymers, especially polyolefins.

3 Claims, No Drawings ALIPHATIC ESTERS OF CARBOXYMETHENE- ANDCARBOXYETHENETHIOSUCCINIC ACID This is a division, of application Ser.No. 191,49l filed Oct. 21, I971, now abandoned.

BACKGROUND OF THE INVENTION Aliphatic esters of thioalkionic acids areknown as antioxidants for polymers. Thiodipropionic acid esters of theformula are well known wherein R, is an aliphatic group such as analkyl, alkoxy, or thio ether. A Belgium Pat. No. 631,163, disclosescompositions of the formula wherein R,, is an alkyl group containing 12to 18 carbon atoms and R, is an alkyl group containing 1 to 18 carbonatoms or an aryl group such as phenyl, benzyl, and alkyl substituentsthereof. Although the thioalkionic acid esters may be used alone, theyare usually used in combination with phenols. Such combinations havebeen used in polyolefin polymers.

The effectiveness of the phenol/sulfur-containing acid ester combinationis limited by the sulfurcontaining compound itself. For example, whenusing the thiodipropionic acid esters with a set level of pheno]. theprotection to oxidation increases relative to the amount ofsulfur-containing acid ester, at least up to levels of 1.0 parts byweight or more. As such, it is desirable to use higher levels. But,these compounds start to bloom from polyolefins at levels as low as 0.25parts per hundred of polyolefin, and at a level of 1.0 parts per hundredbloom readily. Also, when used at 1.0 parts per hundred, thethiodipropionic acid esters can adversely affect the ultra-violet (UV)light resistance of the polyolefin, lowering the resistance by as muchas There is a need for a sulfur-containing acid ester that will provideimproved oxidative protection for polyolefins, and that will not bloomfrom or adversely affect the UV resistance of polyolefins.

SUMMARY OF THE INVENTION The invention providesnovel aliphatic esters ofearboxymetheneand carboxyethcnethiosuccinic acid. Such compounds areparticularly useful in providing protection against oxidation ofpolymers, especially polyolefin polymers. The compounds are used alongor alone phenol antioxidants.

DETAILED DESCRIPTION The novel sulfur-containing acid esters arealiphatic esters of carboxymetheneand carboxyethenethiosuccinic acid.The compounds are named following definitions as found in LangesHandbook of Chemistry, Revised th Edition 1967). Page 336, whereinmethene is defined as (-CH ethene as (CI-I CH and earboxy as (-COOH).The formula for these comwherein R R and R are selected from the groupconsisting of an alkyl group containing 8 to 24 carbon atoms, an alkoxyalkyl group containing a total of 6 to 12 carbon atoms, and an alkylthioalkyl containing a total of 6 to 12 carbon atoms, and n is l or 2.The alkyl groups can be linear or branched, i.e., can contain primary,secondary, or tertiary carbon structures. Preferably the R group is analkyl group of linear structure containing from about 10 to about 18carbon atoms. Examples of such groups are decyl, dodecyl, pentadecyl,tetradecyl, octadecyl, and the like.

PREPARATION The carboxymetheneand carboxyethenethiosuccinic acid estersare readily prepared in a two-step process. In the first step,mercaptoacetic or mercaptopropionic acid is. reacted with butenedioicacid, its cisanhydride, the aliphatic esters thereof or the alkali metalsalts thereof. The cis form of butenedioic acid is commonly calledmaleic acid, the trans form is called fumaric acid, the cis anhydride iscalled maleic anhydride, and the esters are called maleatcs andfumarates. The intermediate formed in step one is esterified in step twoto yield the desired tris ester products.

The following paragraphs disclose the process in more detail. Specificdisclosure is made to the reaction of mercaptoacetic acid with maleicacid to form the trisacid intermediate, which is then reacted with amonohydric aliphatic alcohol to form the tris ester product. It is to beunderstood that the following process can also employ mercaptopropionicacid and/or fumaric acid, and also maleic anhydride and aliphaticmaleates and fumarates in place of the maleic or fumaric acid.

The first step of the process comprises the addition reaction ofmercaptoacetic acid to maleic acid in the presence of a base catalyst.Although a molar excess of any one of the reactants may be employed, itis preferred to use an essentially equimolar level of each reactant asthis makes recovery and purification easier.

The base catalyst can be an inorganic base such as sodium and potassiumhydroxide; an alkali alcoholate such as sodium methoxide, potassiumbutoxide, and the like; an amine such as ammonia, ethylamine,butylamine, diethylamine, pyridine, piperidine, triethylenediamine, andthelike; and quaternary ammonium hydroxides such as tetramethyl ammoniumhydroxide, dimethyl ethanol benzyl ammonium hydroxide, trimethylbenzylammonium hydroxide, and the like. Preferred are the strong organicbases, and most preferred are the quaternary ammonium hydroxides. Thebase is used in catalytic amounts, ranging from about 0.001 moles toabout 0.02 moles per 1 mole of mercaptoacid.

A solvent for the step one reaction may be used. Typical solvents arearomatic hydrocarbons such as benzene, toluene, xylene, and the like,and dioxane and tetrahydrofuran.

The reaction temperature is from about C. to about 100C. Reaction timeis from about 0.5 hours to about 6 hours. The reaction betweenmercaptoacetie acid and maleic acid produces carboxymethenethiosuceinicacid. Yields in excess of 60% conversion of reactants, to as high as90%, are obtained.

If maleic anhydride or a dialiphatic maleate were used in place ofmaleic acid, the products would be carboxymethenethiosuceinie anhydrideand carboxymethenethiosuccinie acid (dialiphatic) ester respectively.The use of mercaptopropionic acid in place of mereaptoacetic acid wouldproduce carboxyethenethiosuccinic acid.

The trisacid produced in step one is reacted in step two with amonohydric aliphatic alcohol, in the presence of an acid catalyst, toproduce the trisester prod' ucts. Although an excess of one of thereactants may be employed, it is preferred to use essentially threemoles of monohydric alcohol to every one mole of trisacid. This molarratio applies if the step one product is the acid-anhydride productalso, but if the step one product is made from a maleate or fumarate,thereby having one or more acid groups already esterified, the ratioshould be adjusted accordingly. If the step one product already hasester groups, inter-ester exchange can occur in step two.

The monohydric aliphatic alcohols used are of the formula R-OH wherein Ris selected from the group consisting of an alkyl group containing 8 to24 carbon atoms, an alkoxy alkyl group containing a total of 6 to 12carbon atoms and an alkyl thioalkyl group containing a total of 6 to 12carbon atoms. The alkyl group may be linear or branched, i.e., cancontain primary, secondary, or tertiary carbon structures. Preferably,the R group is an alkyl group of linear structure containing about toabout 18 carbon atoms.

Examples of monohydric aliphatic alcohols are 1- octanol, l-nonylalcohol, 7-methyl-1-oetano1, 1- decanol, l-dodecanol, l-pentadecanol,l-tetradecanol, l-octadecanol, and the like; and 4-methoxy-1-hexanol,5-methoxy-2-methyll -pentanol, 7-methoxy-1- heptanol.3-ethyl-4-ethoxy-l-pentanol, 8-methoxy-1- octanol, l0-ethoxy-l-decanol,and the like; and 4-methylthio'l-hexanol, 8-ethylthio-1-octanol, and thelike. Examples of the preferred alcohols would be 1- decanol,l-dodecanol, l-pentadecanol, l-tetradecanol, l-octadecanol, and thelike. Normally only one type of alcohol is used, but mixtures thereofmay be employed.

The acid catalyst employed can be any strong organic or inorganic acid.Excellent results are obtained when a strong organic acid is used.Examples of strong organic acids are o-sulfobenzoic acid, dodecylbenzenesulfonic acid, p-toluene sulfonic acid, and the like. The amount of acidused is catalytic, ranging from about 0.001 moles to about 0.02 molesper mole of trisacid.

The acid may be conveniently added to the reaction solution of step one.In this case the acid first neutralizes the base catalyst of step one,and then an excess is added to act as the catalyst for step two. Afterthe acid addition, the alcohol and a solvent are added, and step two ofthe process can be conducted without having to recover the trisacidintermediate of step one.

UTILITY The carboxymetheneand carboxyethenethiosuccinic acid esters areuseful in providing oxidative protection for organic materials subjectto oxygen attack. Such organic materials can be fatty oils and fats,waxes, triglycerides, and the like, but more typically are olefinicpolymers having a molecular weight from about 1000 to about one millionor more. These olefinic polymers can be saturated polymers or copolymerssuch as the polyesters, polyvinyl halides, polyvinyl alcohols,polymonoolefins, and the like; or dienic polymers or copolymers such asthe polybutadienes, polyisoprenes, styrene-butadiene polymers,butadiene-acrylonitrile polymers, and the like. Alternately, theolefinic polymers can be copolymers of monoand diolefinie monomers suchas the ethylene-propylene-diene polymers wherein the diene can be1,4hexadiene, dicyclopentadiene, ethylidene norbornene, and the like.

The compounds have particular utility in providing oxidative protectionfor polymonoolefin polymers and copolymers. Examples of such arepolymers of a-monoolefin monomers such as ethylene, propylene,isobutylene, l-butene, l-pentene, l-hexene, 4-methyll-pentene, and thelike. Polymers of ethylene, propylene, isobutylene, l-butene, mixturesthereof, and mixtures with diene monomers are the most common. Suchpolymers typically have molecular weights ranging from about 3000 toabout 20,000 or more.

A solvent need not be used in step two of the process, but preferably anaromatic hydrocarbon like benzene, toluene or xylene is used. Thereaction temperature ranges from about 50C. to about 150C. A convenientmethod of conducting the reaction is to run the reaction at the refluxtemperature of the solvent. In this manner the water formed in theesterification can be trapped and removed from the system, therebydriving the reaction to further completion. The esterification takesfrom about 5 hours to about 20 hours.

The trisester products, which are low melting solids, are recovered byevaporating the solvent and unreacted ingredients off under reducedpressure. The compounds can be purified by recrystallizing them from anether-methanol solution and washing the product with dilute hypochloritebleach to remove trace mercaptan odors. Yield of trisester product inexcess of con version of reactants, and up to 98% conversion, areobtained.

The carboxymetheneand carboxyethenethiosuccinic acid esters are used inthe amounts from about 0.05 parts to about 7.5 parts by weight basedupon 100 parts by weight of the polymer. More typically, they are usedin the range from about 0.1 parts to about 3 parts by weight. Excellentresults are obtained when they are used at 1.0 parts by weight incombination with a phenol antioxidant.

Any of the known phenol antioxidants can be employed with the compoundsof this invention. Typical examples of phenols are the monohydricphenols such as 2,6-di-tert-butyl para cresol, 2,4-diethyl phenol,2,4,6-trihexyl phenol, the stearyl ester of 4-carboxyethene-Z,-di-tert-butyl- 1 -hydroxy benzene, and the like; andthe polyhydric phenols of the formula and CH --R wherein R,., R R R,,are H, an alkyl group of linear or branched structure containing 1 to 18carbon atoms, an alkoxy group containing 2 to carbon atoms, or a hydroxygroup, and R can further be a ring structure of the formula A Thecarboxyrnetheneand carboxyethenethiosuccinic acid esters and the phenolscan be admixed with the olefin polymers using standard mixing equipmentsuch as roll mills, banburys, extruders, and the like. A preferredmethod of mixing comprises dissolving the antioxidants in a solventadding the solution to a polymer slurry, and then evaporating off thesolvent(s).

The following examples serve to more fully illustrate the invention.

EXAMPLE I A series of step one reactions was made in whichmercaptoacetic acid was reacted with maleic anhydride to formcarboxymethenethiosuccinie anhydride. The recipes, reaction conditions,and percent product yields based on the reactants were as follows:

Malcie anhydride.

moles Mercaptoacetie acid. moles Trimethylhenzyl ammonium hydroxide.moles Triethylene diamine. moles Dioxane, milliliters Benzene,milliliters Reaction Temp. C. Reaction Time,hours Percent Product Yield0,] 0. l 0. l 0.1 ().l 0. l

wherein R R,,-, R,,, and R,, are H or an alkyl group of linear orbranched structure containing 1 to l8 carbon atoms.

The polyhydric phenols are preferred over the monohydrie phenols.Examples of polyhydric phenols are 4,-

4'-thiobis(2-tert-butyl-6-methyl phenol), 4,4-nbutylidenebis(2-tert-butyl-5-methyl phenol), 4,4- butylidenebis( 3-meth\'l-6-tert-butyl phenol), 4,4- cyclohexylidenebis( Z-tert-butyl phenol),4,4',4-

trimethylphenyltris(2,6-di-tert-butyl para cresol), l,3.- 5-tris(3,5-di-tert-butyl-4-hydroxybenzyl )isocyanurate and the like. US. Pat.No. 3,157,517 discloses more examples of useful phenols.

The phenols are used in the levels from .about 0.01 part to about 5.0parts by vweight, and more preferably from about 0.1 part to about 3parts by weight based upon parts by weight of polymer.

The maleic anhydride, the mercaptoacetic acid, 0.1 grams of basecatalyst, and 200 milliliters of solvent (if used) were charged to areactor vessel equipped with a stirrer, a condenser and thermometer. Thesolutions were heated and stirred for the indicated times. The product,a solid, was recovered by direct drying under reduced pressure. A smallportion of the product was hydrolyzed to the trisacid and analyzed byInfra-red and melting point to characterize it.

Reactions were also run using mercaptopropionic aeidin place ofmercaptoacetic acid. The product was carboxyethenethiosuccinieanhydride.

Reactions were run using the dodecyl ester of maleic acid. The productswere carboxymetheneand carboxyethcnethiosuccinic acid (dodeeyl) ester.

The above products were esterified, using 1- octadecanol in the presenceof p-toluene sulfonic acid as the catalyst, to make the desiredtrisester compounds.

EXAMPLE II A series of runs was made inwhich the step two esterificationreaction was conducted in the same reactor vessel immediately followingthe step one reaction. Recipes, reaction conditions, and percent productyields were as follows:

appearance of carbonyl absorption is observed. The time to failure ismeasured as the time indicated by the intersection of two straightlines, one drawn to the slope of the initial absorption readings (almosta horizontal line) and one drawn to the slope of the rapid absorptionreadings. With the onset of rapid carbonyl appearance, the PE becomesembrittlcd.

Included in the valuation were PE sample (X) containing a thiodialkionicacid ester and PE sample (Y) The maleic anhydride, the mercaptoaceticacid, the trimethylbenzyl ammonium hydroxide, and the solvent (if used)were charged to a reactor vessel equipped with a stirrer, a condenserwith a trap, and a thermometer. The solutions were heated to reflux andstirred for the indicated times. After cooling, the p-toluene sulfonieacid, l-octadeeanol, and solvent (if used) was added to the solution.They were then again heated to reflux for the prescribed times. Thetriester product, a solid, was recovered by direct drying under reducedpressure. The compounds were purified by recrystallizing them fromether-methanol solutions. The product was characterized by Infra-red andmelting point analysis.

When mercaptopropionic acid was used, the product was the trisoctadecylester of carboxyethenethiosuccinic acid. When other monohydric aliphaticalcohols are used in place of l-octadecanol, the corresponding trisesteris obtained.

EXAMPLE III Trisester compounds of this invention were evaluated, incombination with various phenols, as antioxidants for a high densitypolyethylene polymer sold commercially as Petrothene (U.S. Industries).The antioxidants were added to the polyethylene (PE) by dissolving boththem in acetone, adding the solution to a slurry of PE in acetone, andthen evaporating off the acetone under reduced pressure. The PE was thenmilled for 5 minutes on a 300F. roll, sheeted, and put into molds for 5min. at 300F. Test samples were prepared by cutting 1 X 2 inch strips ofabout 25 mil thickness. The PE samples were evaluated by mounting themin a circulating air oven at 125C. and observing the formation ofcarbonyl groups which is evidence of oxidation. This was done byperiodically measuring the Infra-red absorption of the test samples inthe l5002000 cm region. A plot of absorption versus time in hours ismade. Testing is continued until rapid containing a compound of theBelgium patent composi- 0 tion. Results were as follows:

COOR;, wherein R is an octadecyl group and R and R, are dodccyl groupstrisester of the formula: R,OOCCH CH -S-CHCH OOR COOR wherein R, is anoctadecyl group and R and R are dotlccyl groups distearyl ester ofthiodipropionic acid ditlodecyl ester of dodecylthiosuccinic acidstcaryl ester of 4-carboxyethene-lo-di-tert-butyll-hytlroxy benzene4.4-thiobis(Z-tcrbhutyl-(w-methyl phenol) parts by weight per l00 partsby weight of polyethylene The results show that the compounds of thisinvention far out-perform the other sulfur-containing acid esters.

EXAMPLE IV The trisoctadecyl ester of carboxyethenethiosuccinic acid wascombined with a phenol and evaluated as an antioxidant for apolypropylene polymer sold commer- 65 cially as Prof-ac 6501 (Hercules,Inc). The antioxidants were dissolved in benzene and added to a slurryof polypropylene (PP) in benzene, and the benzene evaporated off underreduced pressure. The PP powder was Sull'ur Phenol Compound pph" pph"Hours at I4()C.

C 0.25 ().l 3336' 0.25 0.25 4080" L 0.] XI 12 X 0.25 0.] 40] 2" 0.250.25 4348" l.() ().l M

Y 0.25 (Li 3036 0.25 0.25 3132 'trioetutleeyl ester ofcarboxyethenethinsuccinie acid l .3.5-tris( .i ,5-di-tert-hutl-4-hydrnxybenzyl )isoeyanurate parts by weight per hundred parts yweight of polypropylene average value of three tests The data shows thatthe compound of this invention out-performs the other sulfur-containingacid esters. This is particularly significant in view of the fact thatthe trisesters of this invention do not bloom while the distearyl esterof thiodipropionic acid (compound X) bloomed readily at 1.0 part perhundred.

EXAMPLE V Polypropylene samples prepared similarly to those in ExampleIV were tested for their Ultra-violet (UV) light resistance. The sampleswere mounted in a Xenon Lamp Weather-Ometer at about 40C. Periodically,they were checked for carbonyl absorption and evaluated following theprocedure in Example III. As a control, a polypropylene samplecontaining only the phenol was evaluated. Results were as follows:

Sulfur (ompph pph of PhenoP Hours Percent Change pound none ().l 530 D'0.25 ().l 660 l.() 0.] 647 22 C (1.25 (L1 645 1.0 (LI 676 27 X 0.25 0.]570 trisoctadeeyl ester of earboxymethenethiosuccinic acid 2 l.3.5-tris( 3.S-tli-t-butyl-4-hydroxybenzyl )isueynnurate The data showsthat the thiodialkionic acid esters adversely affected the UV resistanceof the polypropylene when used at levels which yielded good oxidativeprotection in the heat aging tests. In contrast, the trisesters of thisinvention, when used at the same levels, not only exhibited better heataging stability but actually improved the UV resistance of thepolypropylene.

Although the specification and examples are drawn to the use of thetriester products in polyolefins, they can also be readily used toimprove the oxidative stability of other polymers and high molecularweight organic compounds. Examples of such are dienic polymers such asethylene-propylene-diene polymers, styrene-butadiene polymers,butadiene-acrylonitrile polymers, and the like; saturated polymers suchas polyesters, polyvinyl chlorides, polyvinyl alcohols, and the like;and fatty oils and fats such as cottonseed oil, linseed oil, corn oil,olive oil, sardine oil, tall oil, and the like, and lard, waxes,glycerides and the like.

I claim:

1. A composition comprising a poly-a-monoolefin polymer, about 1 part byweight of a compound of the formula wherein n l or 2, and R R and R arealkyl groups containing 8 to 24 carbon atoms and from 0.01 part to about5 parts by weight of l,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, all weights based upon parts by weight ofpolymer.

2. A composition of claim 1 wherein the poly-aolefin polymer is selectedfrom polyethylene and polypropylene, and wherein said compound n 2 and RR and R are alkyl groups containing from about 10 to about 18 carbonatoms in the group.

3. A composition of claim 2 wherein said compound R R and R areoctadecyl.

1. A COMPOSITION COMPRISING A POLY-A-MONOOLEFIN POLYMER, ABOUT 1 PART BYWEIGHT OF A COMPOUND OF THE FORMULA
 2. A composition of claim 1 whereinthe poly- Alpha -olefin polymer is selected from polyethylene andpolypropylene, and wherein said compound n 2 and R1, R2, and R3 arealkyl groups containing from about 10 to about 18 carbon atoms in thegroup.
 3. A composition of claim 2 wherein said compound R1, R2, and R3are octadecyl.